Groundwater is a vital resource, which, if goes unprotected, can become a permanent destination for pesticides. As a precious component of our environment, protecting groundwater should be a high priority when applying pesticides. Protecting groundwater can be accomplished by a constant awareness of soil characteristics, including texture and structure. A second method you must practice is proper applicator methods. By incorporating these techniques into your pest-control program, you can protect that liquid treasure known as groundwater.

Beneath The Surface
Groundwater is located within soils, below the earth’s surface, moving slowly through rock and soil particles. Groundwater also can be found in limestone areas where it can flow through large underground canals or caverns. As compared to surface water, which moves rapidly over ground, groundwater moves slowly — sometimes only a few feet in a month. Groundwater is capable of providing large amounts of water known as an aquifer. Aquifers provide us with drinking, washing, and irrigation water by providing water to a well. If pesticides find their way to aquifers through the process of leaching, there is a potential for contamination of the water people use every day for living.

Standing water will eventually leach to groundwater.

Leaching is the vertical movement of pesticides through the soil as opposed to horizontal movement over the earth’s surface. Some pesticides are more likely to leach as a result of their chemical and physical properties. These leaching properties include solubility, adsorption, and persistence. For example, if a pesticide is held strongly on the surface of soil particles by adsorption, it is less likely to leach. Solubility is a second factor if you are using a pesticide that easily dissolves in water. It can easily move with water in the soil. Persistence, or how long it takes a pesticide to break down in the environment, also has an influence on leaching. If a pesticide is rapidly broken down, it is less prone to leaching because it remains in the soil for short periods of time. These three factors are all interrelated. Pesticides that are most likely to move into groundwater are extremely soluble, highly persistent, and are not tightly attached to the soil. Information on solubility, adsorption, and persistence of pesticides will sometimes not be found on the pesticide label. If that is the case, contact the manufacturer and ask for that information.

Sifting Through Soil
Soil characteristics or properties also are an important factor in the breakdown and movement of pesticides. These factors include texture, structure, permeability, and organic matter.

Soil texture is a term generally used to describe how different sizes of mineral particles such as sand, silt and clay are distributed in the soil. Soil particles range in size from very coarse sand to clay and are separated into groups according to their size. Coarse or sandy soils allow water to carry pesticides quickly downward, while textured soils slow pesticide movement.

Soil structure indicates how the soil particles are combined. If a soil is made up of mostly sand particles, there is likelihood for increased downward movement of water through the soil. Soils that permit a rapid flow of water are more likely to present a greater chance of groundwater contamination compared to coarse textured or compacted soils.

Permeability measures how rapidly water can move downward through the soil and is influenced by both soil texture and structure. Soils that are sandy or coarse are by and large considered more permeable and again have a greater tendency for groundwater contamination.

Organic matter has an enormous influence on how much water the soil will hold before moving downward. Organic matter also influences adsorption of pesticides to the soil. Soils that are high in organic matter have an ability to hold more water in the soil profile, making less water available for leaching. Soils rich with organic matter also can adsorb or bind many pesticides to the soil surface, reducing the rate of downward movement toward groundwater.

The Applicator’s Role
As an applicator, there are a number of practices you can incorporate for a common-sense approach to the prevention of pesticide leaching.

If pesticides find their way to aquifers through the process of leaching, there is a potential for contamination of the water people use every day.

Monitor weather conditions. Intense amounts or prolonged periods of rain can cause water to rapidly flow through the soil structure. By monitoring the weather, a pesticide application can be prevented from polluting groundwater. Applying pesticides before a scheduled irrigation also can contribute to leaching. By carefully monitoring the amount of irrigation that is being applied, you can decrease the amount of pesticide leaching.

Go with the flow. By understanding how pesticides move with water and through soils you can prevent the leaching of pesticides to groundwater. Visit the University of Florida/Institute of Food and Agricultural Sciences’ (UF/IFAS) “Solutions For Your Life” Web site at http://solutionsforyourlife.ufl.edu/ or contact your local county Extension for more information.

Integrated Pest Management (IPM) takes into account the use of chemical, cultural, and biological control by placing these elements into one cohesive program to manage pests. Identification is the key to a successful pest management program. Through the use of an IPM approach, pesticide applications can be minimized, reducing costs and protecting groundwater. Maintaining a portable library of pest identification books and pocket flip cards is an excellent first step toward accurate identification.

Proper application is the key to an effective pesticide program. Keep the application on the target site. Never exceed recommended application rates. By carefully calibrating application equipment, the applicator can be assured that rates are remaining within the desired application levels. Accurate calibration will prevent excess pesticides from leaching their way into groundwater.

Mix and load cautiously. Your mixing/loading site should be as close to your pesticide storage building as possible. Both the building and the mixing/loading site should be located at least 300 feet from a well. When mixing, the use of an impervious chemical rinse pad or moveable plastic pad is a good idea.

Use common sense when pitching pesticides. When disposing of pesticides, follow label instructions. If there is any excess spray mix, apply it to crops listed on the label. Do not drain the material onto the ground, always mix and load pesticides carefully, and try to avoid mixing too much. Try to purchase the correct amount of material needed for the job. To dispose of empty pesticide containers, first triple rinse and then dispose of them in accordance with the label.

Ed Skvarch is a commercial horticulture educator at UF/IFAS St. Lucie County Extension Office in Ft. Pierce, FL.